The Distribution of Vegetation in the United States: As Related to Climatic Conditions

The Distribution of Vegetation in the United States: As Related to Climatic Conditions

Excerpt

This publication constitutes an attempt to correlate the distribution of the vegetation of the United States with the distribution of some of the climatic conditions that appear to be most important to plants. It has long been a matter of common information that such a correlation exists, and some of its most obvious features have commanded popular attention from the earliest settlement of the country. The influence of a low and uncertain rainfall in inhibiting the occurrence of trees in certain portions of Kansas and Nebraska, for example, and the influence of the high winter precipitation of the Pacific Northwest in permitting the occurrence of a heavy forest in that region, are matters that have come to the attention of every one familiar with those regions. It has been the aim of our work to make a somewhat thorough investigation of such correlations as these by bringing together a carefully elaborated set of climatological data and a representative set of data with respect to the occurrence of certain characteristic species of plants, in addition to the facts of the distribution of typical vegetations. We have sought, by appropriate means, to ascertain the extremes of each climatic feature for each of the vegetational or distributional areas. In short, we have determined the maximum and minimum values of each climatic feature for such well-known regions as the Great Plains, the Gulf pine-belt, or for such well-known species as the Sitka spruce (Picea sitchensis), the sage-brush (Artemisia tridentata), and the small cane (Arundinaria tecta).

Our desire is not only to set forth the basal facts upon which we have worked and such features of correlation as we have been able to discover, but also to clarify some of the conceptions fundamental to such work and to stimulate a greater interest in it. It is particularly desirable that our work should be regarded as a preliminary and extremely general investigation of this subject for the United States, and that more exact studies of smaller areas should be carried out in order to study more thoroughly the relations with which we have dealt. It will of course be possible to use the climatological data which we have gathered for the study of other subdivisions of the vegetation than those that we have used and for the determination of the climatic controls for other species than those we have selected. It is also to be hoped that the United States Weather Bureau and other agencies will make it possible, at no distant date, to draw other climatic maps than those we have been able to construct from the data now available.